1. Field of the Invention
The present invention relates to a porous cross-linked copolymer and its derivative, and to a process for their production. More particularly, it relates to a porous cross-linked copolymer of chloromethylstyrene and divinylbenzene and a porous iminodiacetic acid type chelating resin, and to a process for their production.
2. Description of the Prior Art
Porous cross-linked copolymer having reactive chloromethyl groups have been produced by a process comprising copolymerizing styrene and divinylbenzene, and then chloromethylating the polymerized product.
But this process employs, as an essential reagent, chloromethyl methyl ether which has suspision of a cancer-causing compound and accordingly, requires severe restrictions on safety and protective equipment. Furthermore, it is difficult to strictly control the chemical structure since the side reaction of forming secondary cross-linking occurs in addition to the desired introduction of chloromethyl groups.
On the other hand, Japanese Patent Application (OPI) No. 3187/1975 and Japanese Patent Application (OPI) No. 47090/1977 disclose processes which employ chloromethylstyrene as the starting material and have dissolved the problem of forming secondary cross-linking. However, the derivative having properties sufficient for practical uses cannot be obtained.
Various kinds of functional polymers, for example, strongly basic anion exchange resins, weakly basic anion exchange resins, chelating resins and redox resins are synthesized from the intermediate, i.e. the cross-linked copolymer having reactive chloromethyl groups. Some of them are commercially available.
The representative example of them is a chelating resin where an iminodiacetic acid group [CH.sub.2 N(CH.sub.2 COOH).sub.2 ] is introduced to the methylene group bonded with the skeletal aromatic nuclus. This iminodiacetic acid type chelating resin is one kind of weakly acidic ion exchange resins and has a greater swelling ratio than that of other strongly acidic ion exchange resins and other strongly basic ion exchange resins. In this connection, for example, the swelling ratio is about 1.40 to about 1.90 as the volume ratio of H type to Na type with iminodiacetic acid type chelating resins which are commercially available; about 1.03 to about 1.11 as the volume ratio of Na type to H type with strongly acidic ion exchange resins; and about 1.10 to about 1.25 as the volume ratio of Cl type to OH type with strongly basic ion exchange resins. Generally, with greater swelling ratios, the strength of the resin decreases and various disadvantages at practical operation such as a large consumption of resin are brought about.
Thus, a chelating resin having a small swelling ratio and a high mechanical strength is desired for a process using a packed column or using a strongly electrolytic solution. Some kinds of iminodiacetic acid type chelating resins are commercially available, but they are not satisfactory for the industrial use.